Since laminated glass generates only a small amount of scattering glass fragments even when subjected to external impact and broken, laminated glass is excellent in safety. As such, the laminated glass is widely used for automobiles, railway vehicles, aircraft, ships, buildings, and the like. The laminated glass is produced by sandwiching an interlayer film for laminated glass between two glass plates.
Examples of the interlayer film for laminated glass include a single-layered interlayer film having a one-layer structure and a multi-layered interlayer film having a two or more-layer structure.
As an example of the interlayer film for laminated glass, the following Patent Document 1 discloses a sound insulating layer including 100 parts by weight of a polyvinyl acetal resin with an acetalization degree of 60 to 85% by mole, 0.001 to 1.0 part by weight of at least one kind of metal salt among an alkali metal salt and an alkaline earth metal salt, and a plasticizer in an amount more than 30 parts by weight. This sound insulating layer can be used alone as a single-layered interlayer film.
Furthermore, the following Patent Document 1 also describes a multi-layered interlayer film in which the sound insulating layer and another layer are layered. Another layer to be layered with the sound insulating layer includes 100 parts by weight of a polyvinyl acetal resin with an acetalization degree of 60 to 85% by mole, 0.001 to 1.0 part by weight of at least one kind of metal salt among an alkali metal salt and an alkaline earth metal salt, and a plasticizer in an amount of 30 parts by weight or less.
The following Patent Document 2 discloses an interlayer film which is constituted of a polymer layer having a glass transition temperature of more than 33° C. In Patent Document 2, a technique of arranging the polymer layer between glass plates with a thickness of 4.0 mm or less is described.